JPH04266603A - Control circuit for distributing pressure medium flow regardless of load - Google Patents

Abstract

PURPOSE: To make a pressure difference adjustable to keep the speed-based change of consumer motion independent of action on the directional control valve of a consumer in a control circuit of an excavator or the like by providing upstream of the directional control valve a pressure balancer which is actuated in relation to the pressure difference between upstream and downstream of the directional control valve, a pump, and the pressure difference of maximum load pressure. CONSTITUTION: When the load pressure of a consumer 13 is higher than the load pressure of a consumer 14, the higher load pressure is transmitted to a pressure balancer 9 by a conduit 22a to produce the same load pressure within a conduit 19b. Pump pressure within a conduit 7a produces pump pressure corresponding to maximum load pressure. This pressure produces opposite pressure in the upstream conduit 24 of a directional control valve 11, producing a pressure balance in the pressure balancer 9, which is kept open. Then the pressure balancer 10 of the consumer 14 is loaded with the load pressure of the consumer 13 via a conduit 22b and the pressure balancer 10 produces pressure balance and moves in an opening direction, producing a throttling effect and producing a pressure difference at the directional control valve 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION The present invention relates to a control circuit for load-independent distribution of a pressure medium flow to a plurality of consumers connected to a hydraulic pump and consuming hydraulic energy. The consumers can each be operated by a directional control valve which produces a throttling effect in an intermediate position, and a pressure balancer is connected upstream of the directional control valve to regulate the flow of pressure medium to the directional control valve. operates in conjunction with a first pressure difference derived from the pressure upstream of the directional control valve and the pressure downstream of the directional control valve, and a second pressure difference derived from the pump pressure and the maximum load pressure. Concerning the types of things that are possible.

0002

BACKGROUND OF THE INVENTION A control circuit of the above type is known from German Patent Application No. 34 22 165 and is combined with a demand flow regulator. For this purpose, the pump usually has a delivery volume regulator, which regulates the demand flow. A demand flow regulator acts on the pump's delivery volume regulator in relation to the energy required by the consumer. Therefore, the actually required amount of pressure medium is delivered by the pump, thereby avoiding circulation losses and throttling losses.

If the consumer is not activated because the associated directional control valve is in the closed position, the pump exclusively discharges leakage oil, that is to say in the position of minimum adjustment of the delivery volume, The magnitude of the volume or the magnitude of the discharge pressure is determined by a regulating spring acting on the demand flow regulating device. The demand flow regulating device has two control pressure chambers, one control pressure chamber being loaded with the pump pressure and an oppositely acting control pressure chamber being loaded with the maximum consumer pressure and a regulating spring; The adjustment spring is designed to produce a spring force corresponding to a pressure of, for example, 20 bar.

While the consumer is not activated and the control piston is in the null position in the directional control valve associated with the consumer, the pump is operated such that the pump pressure acting on the demand flow regulator is opposite to the demand flow regulator. Pressure medium is discharged only to the extent that it balances with the side springs.

By movement of the control piston of one directional control valve connected upstream of the consumer, the consumer and the pump are connected and the pump pressure is transmitted to the consumer. In this case, the opening opened in the directional control valve by the movement of the control piston acts as a measuring throttle. at the same time,
The load pressure, i.e. the pressure in the line between the actuated directional control valve and the controlled consumer, loads the spring side of the demand flow regulator via the control pressure line, so that the pump increases its delivery volume. signal to increase the discharge volume and thus the pump pressure.

Due to the increase in pump pressure, the consumer is moved and a pressure difference Δp is created in the measuring throttle. A balance in the system occurs if the pressure difference Δp in the directional control valve corresponds to the spring preload of the demand flow regulator. This automatically adapts the pump discharge flow to the demand flow. The directional control valve belonging to the consumer, or the control piston of the directional control valve, is actuated via a hand lever, the adjustment distance of which is proportional to the amount of delivery medium reaching the consumer, in which case the directional control valve The pressure difference Δp within is always constant. A flow of pressure medium therefore always flows through the measuring throttle, which is dependent only on the position of the control piston and is independent of the load pressure of the consumer.

The demand flow regulator also functions in a large number of consumers by detecting the maximum load pressure by means of an exchange valve train and transmitting it to the demand flow regulator. However, in the case of a large number of controlled consumers, the demand flow regulating device always responds to the maximum load pressure in each case, so that the control edge opening, which acts as a measuring throttle for the directional control valve of the consumer with lower load pressure, is Due to the newly adjusted and increasing pump output, the increasing pressure differences must be compensated and the speed of movement of the numerous consumers must be made uniform even when one consumer is subjected to a shockingly high load. . Furthermore, the ratio of the speeds of movement of the different consumers must be maintained with respect to each other even if the maximum displacement of the pump has already been reached. For this purpose, an auxiliary valve is integrated in the conduit between the pump and the directional control valve, acting as a pressure balancer, so that the control pressure chamber, which is loaded in the closing direction of the auxiliary valve, is affected by the pressure in front of the directional control valve. The control pressure chamber, which is loaded and loaded in the opening direction of the auxiliary valve, is loaded by the pressure between the directional control valve and the consumer supply channel, ie the associated consumer pressure. the auxiliary pressure chambers acting in the closing direction are loaded with the pressure of the consumer, which is loaded with the maximum load pressure in each case;
The auxiliary pressure chamber, which acts in the opening direction, is then loaded with the pressure in the delivery line of the pump. Two pressure differences are therefore created, a first pressure difference being created by the load pressure of the associated consumer and the pressure upstream of the directional control valve with a throttling action in an intermediate position, and a second pressure difference. is caused by the pump discharge pressure and the load pressure of the most loaded consumer. Of course, it is also possible not to create the pressure difference directly in the pressure balancer, but to create it in advance, for example in the form of a controlled pressure, to the pressure balancer and to act there against the force of the spring. In both cases, a pressure balancer compensates for the pressure difference between the associated consumer pressure and the maximum load pressure. The consumer flow is therefore generated in accordance with the cross section of the individual measuring throttle opening.

[0008] Therefore, a directional control valve equipped with a quantity adjusting device has the following characteristics:
As long as the medium flow delivered by the pump corresponds to the medium quantity received by the consumer, the pump flow is distributed in proportion to the throttle opening of the control piston, regardless of the load. If the consumer flow exceeds the maximum delivery flow of the pump, the maximum delivery flow is distributed to the consumers at the rate at which the directional control valves belonging to the respective consumers are opened.

When such a circuit is used, for example, in an excavator, it can be ensured that the trajectory curve produced, for example, by two simultaneously controlled adjusting cylinders, is maintained in all cases and that when the maximum pump delivery flow is exceeded, Only the speed of the adjusting cylinder that describes the trajectory curve is reduced. The ratio of the movement speeds of the controlled consumers is related to the ratio of the throttle openings of the associated actuated directional control valves. In this case, the pressure difference is the same for all directional control valves and corresponds to the regulating pressure difference of the demand flow regulating device. Manual action by the operator on the directional control valve is required to effect a change in the rate of movement of the consumer. In particular, if you want to travel around track curves with high precision, a great deal of skill is required.

0010

SUMMARY OF THE INVENTION The object of the invention is to improve a control circuit of the type mentioned at the outset so that the speed ratio of the consumer movement can be varied by simple means and independently of the action on the directional control valve. The aim is to make sure that the

[0011]

[Structure for Solving the Problems] In order to solve the above problems, the structure of the present invention is such that the pressure difference can be adjusted by at least one pressure balancer.

0012

Effects of the Invention With the above configuration, the pressure balance in the pressure balancer concerned is shifted, and thus the pressure between the pressure balancer and the directional control valve is changed, which causes a change in the pressure difference in the directional control valve, and thus a change in the pressure medium and the directional control valve. A change in consumer speed is produced. An important idea of the invention is that the regulating pressure difference in the at least one pressure balancer is intentionally adjustable, so that the ratio of the speeds of movement of the consumer can be controlled.

In an advantageous embodiment of the invention, the pressure balancer is moved in the opening direction by the pressure derived from the pressure after the associated directional control valve and by the pressure derived from the pump pressure;
It is loaded in the closing direction by the pressure derived from the pressure in front of the directional control valve and by the pressure derived from the maximum output pressure of all the consumers, and the pressure balancer is provided with an active surface for the pressure. A pressure conduit leads to the working surface, and a device for influencing the pressure is connected in at least one pressure conduit. For any change in the discharge flow distribution, one of the four working surfaces defining the balance in the pressure balancer is intentionally changed, which controls the opening or closing force in the pressure balancer and thus the directional control valve. The passage of the pressure medium flow through the measuring throttle formed by the control piston is ultimately controlled.

[0014] In an advantageous embodiment of the invention, the device for influencing the pressure is designed as a pressure reduction valve. The pressure reduction valve can be set at a predetermined value or, in an advantageous further embodiment of the invention, can be adjusted. If the pressure reduction valve is configured to be adjustable, the adjustment can be done remotely.
For example, this can be done electrically, so that the setpoint value produced in the line with the pressure reduction valve can be varied at will by the operator using an electrical regulating device. It is also possible to make such changes under program control.

[0015] In a further advantageous embodiment of the invention, the device for influencing the pressure has a restriction, and downstream of the restriction, a discharge line branches off, in which the restriction is provided. A pressure limiting valve is connected downstream of this throttle. The incorporation of such a restriction provides the same function as a pressure reduction valve. Either the pressure influencing device is arranged in a conduit leading to the pump and this conduit leads to the working surface of a pressure balancer of one consumer, or the pressure influencing device It is arranged in a leading conduit which leads to the working surface of the pressure balancer of one consumer. It is also possible to arrange devices for influencing the pressure in the conduit leading to the pump and in the conduit leading to the maximum consumer pressure. In principle, the flow rate of the pressure medium through the directional control valve can also be controlled by controlling the responsive pressure of the directional control valve, that is to say the pressure in front and behind the directional control valve.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydraulic pump 1 is adapted to vary the delivery volume by means of an adjusting piston 4 movable in an adjusting cylinder 2 against the force of a spring 3. The pump 1 is adapted to suck pressure medium from a tank 5 and discharge it into a discharge conduit 6, which branches into branch supply conduits 7, 8. Branch supply conduits 7, 8 are connected to pressure balancers 9, 10
The pressure balancer is configured as a 2-port, 2-position directional control valve. Connected to the downstream side of the pressure balancers 9, 10 are directional control valves 11, 12 which are held in a neutral position by springs and produce a throttling action in the neutral position, and the directional control valves are configured as cylinder-piston devices in the embodiment. A consumer 13,1 that can be loaded from two sides
Used to control 4.

For this purpose, a directional control valve 11 is connected via conduits 15, 16 to a consumer 13, and a directional control valve 12 is connected via conduits 17, 18 to a consumer 14. . In the controlled state of the consumers 13, 14,
A pressure line 15 or 16, 17 or 18, respectively, which carries the pressure is connected to the line 19 or 20, which in turn carries the load pressure of the consumer. Conduit 19, 2
0 has branch conduits 19a, 20a, which open to an exchange valve (switching valve) 21. Branch conduit 1
The higher pressure occurring in 9a, 20a, i.e. the higher pressure of the consumers 13, 14, is transmitted from the exchange valve 21 via a conduit 22, which conduit is connected to the demand flow regulating valve 23. It leads to one end face. Demand flow adjustment valve 2
3 is connected to a conduit 6a, which is a discharge conduit 6.
It is branching from. A conduit 6 a leads from the demand flow regulating valve 23 to the regulating cylinder 2 on the end side of the regulating piston 4 facing away from the spring 3 . A conduit 6c further branches from the conduit 6a, and this conduit 6c communicates with the other end face of the demand flow regulating valve 23. A compression spring 23a is further arranged on one end face. The demand flow regulating valve 23 has three switching positions. In the first switching position, the conduit 6a is replaced by the conduit 6b,
In turn, it is connected to the adjusting cylinder 2. In the second switching position, both lines 6a, 6b are connected to the pressureless tank 5. In the third switching position, conduit 6a is blocked and conduit 6b is connected to tank 5.

Each pressure balancer 9, 10 has four working surfaces, two working surfaces are arranged so as to act in the opening direction of the pressure balancer, and the other two working surfaces are arranged so as to act in the opening direction of the pressure balancer.
The two active surfaces are arranged to act in the closing direction of the pressure balancer. In the pressure balancer 9, a conduit 19b branching off from the conduit 19 leads to both active surfaces acting in the opening direction. Both working surfaces acting in the opening direction have
A conduit 7a branched from the branch supply conduit 7 communicates therewith. On the working surface of the pressure balancer 9 acting in the closing direction, the conduit 2
A conduit 22a and a conduit 24 branching from 2 communicate with each other,
In this case, the conduit 24 is branched from the conduit 25;
5 connects the pressure balancer 9 to the directional control valve 11.

Similar to the pressure balancer 9, the pressure balancer 10 of the second consumer has four active surfaces;
Two of these active surfaces act in the opening direction and the remaining two active surfaces act in the closing direction. A conduit 20b branching off from the conduit 20 and a conduit 8a branching off from the conduit 8 lead to an active surface of the pressure balancer 10 acting in the closing direction. A line 22b and a line 26, which branch off from the line 22, are connected to the active surface acting in the closing direction, which in this case branches off from a line 27, which connects the pressure balancer 10 to the directional valve 12. Connected. In conduit 7a and conduit 22b there is a pressure reduction valve 28,
29 are arranged.

The mode of operation of the control device described above is as follows: in the inactive state of the consumers 13, 14, the directional control valves are in the neutral position, so that the conduits 15, 16; 17,
18 and 19, 19a, 19b; 20, 20a, 20
b and 22 are pressureless. The pump is constructed in such a way that the spring 3 always tends to bring the adjusting pin 4 into a position corresponding to the maximum displacement of the pump. When the pump 1 begins to pump, a pressure builds up in the conduit 6 because the directional control valves 11, 12 are closed. This pressure is in conduit 6a
, 6c to the second end face of the required amount adjustment device 23. Due to the force of a spring 23a set to a pressure of, for example, 20 bar, the demand regulator 23 is in a third switching position, in which the line 6b is connected to the tank 5. As the pump delivery pressure increases, the required volume regulating device moves to the right in the drawing and finally connects the conduit 6a to the conduit 6b, thus reducing the delivery volume of the pump 1. A pressure balance occurs in the demand regulator between the spring force and the pump delivery pressure. The pump 1 therefore delivers only a small flow of pressure medium in the inactive state of the consumer to maintain a delivery pressure of 20 bar.

When one directional control valve 11 or 12, for example directional control valve 11, is to be activated for controlling the associated consumer, a control piston in the directional control valve is moved, so that pump 1 and A consumer 13 is connected, in which case an arbitrarily selected cross section is opened, and a defined flow of pressure medium is supplied to the consumer and thus a defined speed of movement of the consumer is achieved. When the pump pressure exceeds the load pressure, the consumer 13 is put into motion and a pressure difference Δp is created across the free cross section of the directional control valve 11 by means of the flow of pressure medium. In principle, the free cross section acts as a measuring aperture. A pressure balance in the system occurs if the pressure difference at the measuring throttle corresponds to the spring preload of the spring 23 of the demand flow regulator 23. A change in the measuring throttle opening causes a change in the pressure difference Δp across the directional control valve, and the change in pressure difference is adjusted by the demand flow regulating device 23, so that a constant pressure difference across the directional control valve is always maintained. As a result, a pressure medium flow flows through the measuring throttle that is constant and exclusively dependent on the opening value (speed setpoint), which is independent of the load pressure. The pump discharge flow is automatically adapted to the demand flow.

At the same time as the direction control valve 11, the direction control valve 12,
Therefore, if the consumer 14 is additionally controlled, the higher load pressure, for example the load pressure of the consumer 13, is applied to the exchange valve 2.
1 to the spring side of the demand flow adjustment device 23. Therefore, the directional control valve 1 of the consumer 14 is loaded with low pressure.
The pressure differential at 2 is increased, requiring subsequent adjustment of the directional control valve by the operator to maintain the desired consumer speed. Pressure balancers 9, 10 are provided to equalize changes in pressure difference. During subsequent monitoring, the pressure reduction valve 28,2 to the pressure balancer
The effect of 9 is ignored. Two differential pressures are created in each pressure balancer 9,10. The first differential pressure is in conduit 19
The load pressure guided through the direction control valve 1
1 or 12 is formed on the basis of an interconnection for the pressure occurring in the conduit 24 or 26 upstream. A second differential pressure is created by interconnecting the pump discharge pressure occurring in conduit 7a or 8a to the maximum load pressure occurring in conduit 22a or 22b.

In this embodiment, it is assumed that the load pressure at the consumer 13 is higher than the load pressure at the consumer 14. This high load pressure is transmitted to the pressure balancer 9 via the conduit 22a. Since the same load pressure is present in the conduit 19b on the opposite side, this pressure increases. A pump pressure is generated in line 7a, which pump pressure corresponds to the maximum load pressure increased by Δp. Opposite to this pressure, on the upstream side of the directional control valve 11, the conduit 2
4, which is approximately the same magnitude as the pump discharge pressure. This creates a pressure balance in the pressure balancer 9, which remains open.

The pressure balancer 10 of the second consumer 14 is loaded via line 22b with the maximum load pressure, ie with the load pressure of the consumer 13. An imbalance therefore occurs in the pressure balancer 10, with the result that it is moved somewhat in the closing direction, thereby creating a throttling action which reduces the pressure in the conduit 27 to a predetermined value. , this value is such that a predetermined pressure difference Δp (20 bar in the exemplary embodiment) is achieved in the directional control valve 12. As a result, the directional control valves 11, 12
The pressure difference Δp is the same for both measuring throttles and the consumer flow is the same as the ratio of the measuring throttle openings.

In order to vary the ratio of the consumer flows and thus of the working speeds independently of the cross-section of the measuring throttle opening, according to the invention the influence force acting on the pressure balancer can be varied controllably at will. This can be done on one or both pressure balancers. The pressure reducing valve 28 (which may be configured to be fixedly adjustable or adjustable in predetermined steps or continuously adjustable electrically) is in the adjusting position where it reduces the pressure while the conduit 7a reduce the pump discharge pressure acting on the pressure balancer 9,
As a result, the pressure balancer 9 is actuated in the closing direction, resulting in a throttling effect. Therefore, the pressure occurring in the conduit 25 decreases with respect to the pressure occurring in the conduit 7, and the pressure difference Δp at the directional control valve 11 decreases, with the load pressure unchanged, and thus the speed of movement of the consumer 13 decreases. do.

The pressure reducing valve 29 in the conduit 22b reduces the maximum output pressure acting on the pressure balancer 10 and thus shifts the balance in the direction of opening the pressure balancer 10, insofar as it is in the adjustment position which reduces the pressure. This reduces the throttling effect present in the pressure balancer 10 (
(if the consumer 14 has a smaller output pressure than the consumer 13) or disappears. As a result, the pressure in conduit 27 is not reduced at all or only slightly relative to the pressure in conduit 8;
As a result, the pressure difference across the directional control valve 12 and thus the speed of movement of the consumer 14 increases with the output pressure of the consumer 14 unchanged.

The adjustment of the pressure reduction valves 28, 29 can be done manually or under program control. Conduit 19b, 2
It is clear that pressure reducing valves or other devices influencing the pressure may be provided in 4, 20b, 26.

[0028] Instead of a pressure reduction valve, it is also possible to provide a throttling mechanism. Such a diaphragm mechanism is shown in FIG. In the conduit 7a there is a restriction 30 instead of the pressure reducing valve 28.
is located. A discharge conduit 7b branches from the conduit 7a on the downstream side of the throttle 30. A further throttle 31 is arranged in the discharge conduit 7b, downstream of which a pressure limiting valve 32 is connected. When the pressure limiting valve 32 opens, pressure medium flows into the tank 5 and a pressure difference is created at the restriction 30. The pump discharge pressure reduced by this pressure difference is applied to the pressure balancer 9. In this embodiment, the pressure reduction valve 32 is loaded with a spring force and a maximum output pressure in the closing direction. The aperture widths of the throttles 30 and 31 are determined so that the pressure acting on the pressure limiting valve in the opening direction is always greater than the maximum output pressure, and opening of the pressure limiting valve is guaranteed. To shut down the device, the adjustable spring of the pressure limiting valve is tightened tightly and the pressure limiting valve remains closed.

[Brief explanation of the drawing]

FIG. 1 shows a control circuit according to the invention with two consumers.

FIG. 2 shows a control circuit of another embodiment according to the invention.

[Explanation of symbols]

1 pump, 2 adjustment cylinder, 3 spring, 4 adjustment piston, 5 tank, 6
Discharge conduit, 6a, 6b, 6c Conduit, 7
Branch supply conduit, 7a Conduit, 7b Discharge conduit, 8 Branch supply conduit, 9,10 Pressure balancer, 11,12 Directional control valve, 13,14 Consumer, 15,16,17,18,19,19a,1
9b, 20, 20a, 20b conduit, 21 exchange valve, 22, 22a, 22b conduit, 23 demand flow adjustment device, 23a spring, 24, 25,
26, 27 conduit, 28, 29 pressure reduction valve,
30, 31 Throttle, 32 Pressure limiting valve

Claims (8)

[Claims] 1. A control circuit for load-independent distribution of a flow of pressure medium to a plurality of consumers connected to a hydraulic pump and consuming hydraulic energy, each of the consumers having an intermediate position. A pressure balancer is connected upstream of the directional control valve to regulate the flow of pressure medium to the directional control valve. a first pressure difference derived from the side pressure and the pressure downstream of the directional control valve; and a second pressure difference derived from the pump pressure and the maximum load pressure. Control circuit for load-independent distribution of pressure medium flow, characterized in that the pressure difference is regulated in at least one pressure balancer (9, 10). 2. Pressure derived from the pressure after the directional control valve to which the pressure balancer belongs and pressure derived from the pump pressure in the opening direction and from the pressure in front of the directional control valve; and is loaded in the closing direction by a pressure derived from the maximum output pressure of all the consumers, the pressure balancer is provided with a working surface for the pressure, a pressure conduit leads to the working surface, and a small one pressure conduit (19b, 24, 7a, 22a; 20b, 26,
8a, 22b), a pressure influencing device (28;
30, 7, 31, 32) are connected to the control circuit according to claim 1. 3. Control circuit according to claim 2, wherein the device for influencing the pressure is constructed as a pressure reduction valve (28). 4. Control circuit according to claim 3, wherein the pressure reduction valve (28) is adjustable. 5. Control circuit according to claim 4, wherein the pressure reduction valve (28) is remotely controllable. [Claim 6] The device that affects the pressure is a constrictor (30
), a discharge pipe (7b) branches from the downstream side of the throttle, a throttle (31) is provided in this branch pipe, and a pressure limiting valve is installed downstream of this throttle (31). (3
3. The control circuit according to claim 2, wherein: 2) is connected to the control circuit. Claim 7: Device for influencing pressure (28; 30
, 7b, 31, 32) are arranged in a conduit (7a) leading to the pump, which conduit leads to the working surface of the pressure balancer (9) of one consumer (13). The control circuit according to any one of . 8. A pressure influencing device (29) is arranged in the conduit (22b) leading to the maximum consumer pressure, which conduit is connected to the pressure balancer (10) of one consumer (14). 8. A control circuit according to any one of claims 2 to 7, which communicates with the working surface.